Abstract
Signaling through A2A adenosine receptors (A2AR) regulates T lymphocyte expansion and modulates T cell receptor (TCR)-mediated effector functions in vitro. To understand the role of A2ARs in the regulation of immune response, we investigated the expression levels of this receptor in different functional lymphocyte subsets. Monoclonal anti-A2AR antibody was used to develop a flow cytometric assay to quantify the expression A2ARs on lymphocytes. We report that detectable levels of expression of A2ARs are much higher among T cells than B cells. More CD4+ than CD8+ T cells express A2ARs, but activation of T cells increases A2AR expression, predominantly in CD8+ T cells. No significant differences were found in the proportion of A2AR+ cells between CD8low and CD8high T cells or between TCR/CD3low and TCR/CD3high T cells. Studies of T helper cell subsets (TH1 and TH2) reveal that lymphokine-producing cells are much more likely to express A2ARs than are cells that do not produce lymphokines. These results suggest that A2ARs are variably expressed on T cell subsets and may regulate cytokine production in activated T lymphocytes.
Footnotes
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Send reprint requests to: Dr. Michail V. Sitkovsky, Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bldg. 10, Rm. llN3ll, 10 Center Dr., MSC 1892, Bethesda, MD 20892-1892. E-mail:mvsitkovsky{at}helix.nih.gov
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↵1 Present address: Department of Clinical Laboratory Medicine, Kobe University School of Medicine, 7–5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan.
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↵2 In these experiments we used PMA and ionomycin instead of the anti-CD3 mAb to activate T cells to avoid inconsistencies due to the differences among batches of Ab in their ability to activate T cells and to avoid problems related with polymorphism of human monocyte Fc receptors for murine IgG1.
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This work was partially supported by National Institutes of Health Grant R01HL37942 (to J.L).
- Abbreviations:
- A2AR
- A2A adenosine receptor
- A2AR+
- A2AR-expressing cells
- A2AR−
- A2AR-nonexpressing cells
- HEK/A2AR
- human embryonic kidney cells transfected with human A2A cDNA
- PBMCs
- peripheral blood mononuclear cells, ZM, A2AR antagonist ZM241385
- FCS
- fetal calf serum
- TCR
- T cell antigen receptor
- TCR-CD3high
- high levels of TCR-CD3 expression
- PKA
- cAMP-dependent protein kinase
- I
- calcium ionophore ionomycin
- PMA
- phorbol myristate acetate
- PE
- phycoerythrin
- Received June 3, 1998.
- Accepted December 11, 1998.
- U.S. Government
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